Binary Exchanges of Calcium, Magnesium, and Potassium on Thermally Desorbed Soil

Core Ideas Thermal desorption is used to remediate contaminated soil. Thermal desorption can alter Gibb's free energies. Thermal desorption at 350°C did not change cation selectivity. Thermal desorption (TD) remediates hydrocarbon‐contaminated soil by heating the soil (200–500°C) to volatilize the hydrocarbons, effectively removing the contaminant from the soil. Knowledge of the effects of TD on remediated soil for agricultural crop production are limited, but cation exchange capacity (CEC) and selectivity for cations can be good indicators of plant productivity potential. In this study, the CEC and selectivity of cations of TD‐treated and untreated topsoil and subsoil were compared using binary exchange measurements of Ca–Mg, Ca–K, and Mg–K. The tested soils were illite and smectite‐dominated Mollisols that were collected near an active TD‐remediation site in northwest North Dakota. Vanselow selectivity coefficients and Gibb's free energies (Δ G ex ) were computed. For all three exchanges, significant differences were observed in Δ G ex between the untreated and TD‐treated topsoil. In the Ca–Mg exchange, both the untreated and TD‐treated topsoil preferred Ca, whereas both TD‐treated and untreated subsoils preferred Mg. For the Ca–K and Mg–K exchanges, all treatments preferred K. Cation exchange capacity values were significantly greater in the untreated subsoil of the Ca–Mg exchange and the untreated topsoil and subsoil of the Ca–K exchange than in the TD‐treated soils. The differences may be caused by contrasts in soil organic C and mineralogy. Although CEC and Δ G ex differed between untreated and TD‐treated soils, the cation selectivities were not altered, suggesting that the magnitude of the differences may not require alternative fertility management to retain previous soil productivity.